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It's fall and many kids are headed back to school and they're on the hunt for the perfect book to read. Don't forget to check out our But Why book series. We have two books perfect for young readers about age 8 to 10. Look for Our Llamas Ticklish and Do Fish Breathe Underwater wherever you buy your books. And if you prefer to listen to books, check out the audiobook versions as well. You can find out more at butwhykids.org books.
But Why is supported by Progressive, home of the Name Your Price tool. You say how much you want to pay for car insurance, and they'll show you coverage options that fit your budget. It's easy to start a quote. Visit Progressive.com to get started. Progressive Casualty Insurance Company and Affiliates, price and coverage match limited by state law. This is But Why, a podcast for curious kids from Vermont Public Radio. I'm Jane Lindholm.
On this podcast, we take questions from curious kids like you, and we find interesting folks to give you the answers. On today's episode... I am five years old. I am from Franklin, Wisconsin. And my question is, why do leaves change color in the fall? My name is Isabel. I live in Montclair, New Jersey. I am seven years old. And my question is, how do the leaves on trees change color in the fall?
Hello, my name is Carmel. I'm five years old and I live in Decatur, Georgia. My question is, why do leaves on sweetgum trees turn different colors? Hi, my name is Jolie. I am eight years old and I live in Big Fork, Montana. And my question is, why do leaves change color and fall off the trees in the fall? That's right, leaves. In particular, fall leaves and how trees go from green to fiery red, orange, and yellow.
Last fall, we tackled questions about the changing leaves, but you've been sending us even more questions about them. So this week, we're bringing back our original segment, plus your new questions and a few new answers. My name is Bella, and I live in Chicago. I'm seven years old. I want to know why leaves only change in fall and they stay green in the summer and spring.
Why do the leaves change color in the fall? Why do leaves change color like red, orange, even pink? Why do trees lose their leaves in the fall? That was Emma Jane from Shreveport, Louisiana, and we also heard from Tallulah in Weybridge, Vermont, and Liam in Burlington, Vermont.
Leaves turn in a lot of parts of the world, but here in Vermont, where we make this show, we take fall foliage very seriously. So we were delighted, but not surprised, to get lots of questions about leaves from our fellow Vermonters. For some answers, we met up with this guy. My name's Mike Snyder. I'm the Commissioner of Vermont's Department of Forest, Parks, and Recreation.
Mike got his start as a forester. Foresters are the professionals with extensive knowledge and experience about our forests. And our main job is to take care of forests and to help people interact with forests in healthy and sustainable ways. Before Mike could tell us why leaves turn bright colors in the fall, you have to understand why leaves are green in the first place. Hi, I am Zoe. I am from Germany. I am
I am five years old and my question is, why are leaves green? So, why are leaves green?
This is the most important question because we benefit so much by the leaves being green. All green plants are green because they contain a pigment, which is a chemical that makes a color. The chemical is a very important part of what goes on in leaves that allows leaves to make their own food.
Chlorophyll is the chemical within the leaves that not only makes it green, but allows it to harvest sunlight and use that with water and minerals from the soil to make food for themselves, starches and sugars that they use to grow and live.
And really, that process of photosynthesis is based on chlorophyll being formed in a leaf. And when it's formed in the leaf to allow that making of one's own food, it just happens that it looks green. It is actually reflecting the green wavelengths from the sun. The sun is transmitting electromagnetic radiation onto this planet, which we all receive. It's a beautiful sunny day. That sunshine has many different wavelengths of light,
It's absorbing a lot of the blue and red wavelengths in the process of photosynthesis and reflecting green. And that's what our eye is picking up on, and that's why it looks green to us. It's the reflected wavelengths of light from the chlorophyll within the leaf that look green to us. So the green color of leaves comes from chlorophyll. That's the chemical that allows photosynthesis to happen, the process that plants use to make their own food from sunlight.
Chlorophyll reflects the green wavelengths of light back to us, making leaves and grass and other plants appear green. Now that we know why leaves are green, it will help us understand why they change to red and orange and even brown in the fall.
We know a lot now about the science of fall foliage and the colors and why and how they develop. I want to be clear that we don't know everything, and some of the magic and the mystery of it still exists. That said, much of the science that's been conducted right here in Vermont has helped
helped us understand the process. Why do the leaves turn color in the fall? First, remember, not all of our trees have leaves that turn color. We have some trees that are called evergreens because they remain green throughout the year. Our spruces and pines and firs and cedars...
The rest of the trees, what we call hardwoods or broad-leaved trees, they don't keep their leaves on through the winter. So this is the key. As the summer turns to fall, we notice the days are getting shorter, the amount of daylight. The trees can tell time that way too. And they are triggered by the shortening day length to say, we got to get ready for winter because we're going to drop our leaves later.
Well, they spent all summer building that leaf, creating the chlorophyll in the leaf and refreshing it on a regular basis. That's an expensive kind of machinery, and they've invested a lot in it. So this is in a way of sort of recycling that the tree does. As the days get shorter and the tree kind of knows it's time to prepare for winter, one of the first things it does is it stops making chlorophyll.
that means the green color fades. And what that does is it unmasks a couple of other colors that were there all along but were overwhelmed by the green from the chlorophyll. In the fall, when the nights start getting longer and the days start getting colder, the tree stops making chlorophyll and the green color fades. Those bright colors were there all along. Pretty cool, huh? These pigments, the carotenoids and xanthophylls, are producing yellow and orange colors.
And so when the chlorophyll stops being made, the green color dissipates and that kind of unmasks the yellow and orange colors. Then as the fall progresses and we get some cool nights, not freezing, but cool, it triggers yet another pigment, the anthocyanin pigment, another chemical that creates the red colors that happen later as the tree is advancing towards closing down for winter.
As the reds begin to develop during the fall season, another process is happening where the leaf is actually forming a boundary between where the leaf attaches... the leaf and the twig, where it attaches to the twig. And...
That's signaling kind of the last roll for the leaf before the wind or rain might blow it or push it off the twig. The reason they want to drop the leaf is that these broad-leaved, like maples and beech and elm and birch and cherry, their leaves are not as tough as an evergreen leaf and can't withstand snow and ice. So if they were to keep their leaves on during the winter, it would really damage the plant. Let me stop Mike Snyder for a minute because we need to take a very quick break.
Let's get back to the science of fall foliage, the bright yellows and oranges that the leaves turn in the fall. We've been talking with Mike Snyder. He's a forester here in Vermont. The final step for the tree to get ready for winter is to drop its leaves. The tree has stored up its winter food, and it's ready to let those leaves go.
There are a couple of really good reasons the tree wants those leaves to fall off. For one thing, the tree needs to make space for those new leaves to branch out next spring. But also, leaves can actually be dangerous for trees because they can hold on to snow, which puts too much weight on the tree. Too much snow on a tree makes the branches heavy and they can break.
You might see this if there's ever a really early snowstorm before all the leaves are gone. Those storms are often full of wet, heavy snow, and they can cause a lot of damage to trees. And again, all of it is about the tree knowing that it needs to, it can't run to Florida for the winter. It's going to be here for a Vermont winter, and it wants to be as prepared as possible. So it shuts down the leaf, the green color fades, the other colors emerge, and then eventually the leaf falls, and the tree is not dead anymore.
It's dormant. It's slowing down. It's not going to be producing any food for the winter. It's going to live on what it has stored during the summer. But the leaves for next year have all been packed away in a bud, in all the different buds throughout the twigs. And the next phase is next spring after a long winter when the days begin to get longer again and the temperature starts to rise. The tree says, time to wake up, time to get back to work. And those buds open up.
and leaves, new leaves for next year emerge that were created this year in some cases and then they make new ones as they developed in the next spring. That's called bud break and when the winter ends and the buds on the trees break and new leaves emerge there's also a period of color that happens then because it's a transition time between winter and summer and you see particularly a nice red hue to those early leaves and as the buds are breaking and before they green up.
So we have kind of two seasons of color. The fall season of fall foliage is the most famous because, well, just look around and for those of you on radio, trust me, it's beautiful. In the spring, when those buds start to open and unfurl into new leaves, sometimes you can see that flash of red or orange just before the chlorophyll starts producing and the leaves turn green.
Now, Vermont, where we're based, is very proud of its fall foliage. But Mike Snyder says you can probably see colors near you, too. Wherever there are broadleaf deciduous trees, the ones that have these tender leaves that can't remain through winter and the seasons...
Indeed, you have leaves changing colour. Vermont is heavily forested, about 75% forested, and we have relatively healthy forests. And because of our varied topography and the climate here and the land use history, we do believe that it's the world's best foliage. But sure, other states have trees that turn colours, and it's beautiful there too. Here's one more question from Elliot. My name is Elliot.
I live in Fairfax, Vermont, nine years old. My question is, why don't leaves turn all the colors of the rainbow? Why don't leaves turn all the colors of the rainbow? Good question, Elliot. Leaves turn red and yellow because those are the colors the trees produce. The carotenoids and the xanophils that we learned about earlier are red and yellow. When those chemicals are gone and their colors fade, all that's left are the tannins, and those are brown.
Now, there are plants that have leaves of all different colors, but the ones we're talking about specifically don't produce pigments or chemicals in other colors, like blue or purple or pink. So we don't get leaves that turn all the colors of the rainbow. That's it for this week. But Why is produced by Melody Beaudet and me, Jane Lindholm, for Vermont Public Radio. Our theme music is by Luke Reynolds. What do you want to talk about? Send us a question on any topic.
Have an adult record you on a phone memo function. Tell us your name, where you live, how old you are, and what you want to know. I do want to take a minute here to say that I know it might be hard for some of you to send a question in and not have it answered immediately, or even sometimes at all. I know how that feels.
We have way too many questions to answer them all. But I want you to know that Melody and I listen to all of them. And they help us understand what kinds of things you're interested in and where you might want the show to go. And we love hearing your voices.
By the way, you can always send us your thoughts on what we talked about in an episode you just listened to. What you liked, what you didn't like, what you think we should do differently, or maybe just a story that it sparked from your own experience that you want to tell us about. We love hearing all of the things that you tell us after listening. That's called feedback, and we love it. You can send your questions or your feedback to questions at butwhykids.org.
Anyway, we'll be back in two weeks with an all-new episode. Until then, stay curious. From PR.
